Power-controlling apparatus



Dec. 24, 1929. J, T,"COW| EY' POWER GONTHOLLING APPARATUS Filed Nov, '7. 1928 2 Sheets-Sheet lllilllfflllaltl.

@m by @fr Dec. 24, 1929. J. T. cowLEY POWER CONTHOLLING APPARATUS Filed Nov. '7, 1928 2 Sheets-Sheet UNITE STAT P T "if,

NT 0F EQE JAMES T. COWLEY, OF SYRPICUSE, NEW' YORK, ASSIGNOR TO THE LAIVISON COMPANY, 0F SYRACUSE, NEW YORK, A CGRPORATION 0F MASSACHUSETTS POWEEeCONTROLLING APPARATUS Application filed November 7, 1928. Serial No. 317,858.

This invention pertains to pneumatic despatch systems of the .so-called minimum flow77 vacuum type, and relates more particularly to automatic power controlling appara- 5 tus for use in such a system. Apparatus of this general character-is disclosed in the patent to Libby, No. 968,576, dated August` 30,

1910. The patented apparatus provides au tomatic pressure actuated means for initiat 10 ing carrier impelling air flow through the transmission tube whenever a carrier is inserted therein, and means of cutting off such flow after the lapse of a predetermined period of time.

In said patented device the cessation of carrier impelling air flow is dependent upon the operation of atiining device, but in other controllers of this general character the air fiow is cut oif by devices which are sensitively responsive to the changed conditions in the line occasioned by discharge of a carrier.

Such sensitively responsive devices sometimes act in response to pressure change, and in 2r others to variation in velocity of air flow,

and while in its broader aspects the presentinvention is applicable to devices of both these latter types, I have herein chosen to illustrate it as specifically applied to that type in which the sensitively responsive de 0 vice or detector element is actuated by change in velocity of the air current. Usually this type `of detector takes the form of a vane so disposed in the flowing air current that sudden changes in velocity cause the vane to move 'i from a normal position, and by such imovement to set into action the meansl for closing the controlling` valve. While from a theoretical standpoint such a vane should be dependably operative, it is found in practice that the sudden opening of the controlling valve results in the production of a series fof pulsations or air waves in the tube, and if the controlling vane be suiiiciently sensi-tive to respond to variations in air velocity occasioned by the discharge of a carrier, it may seinetimes respond to the pulsations setup at the opening of the valve, thus producing an erratic behavior of the controller which is ex tremely undesirable.

In accordance ywith the present invention I Cft employ an air actuated vane such as just referred to, but guard against the improvident response of the vane to fluctuations in air velocity during the opening of the controlling valve and for such a length of time thereafter as to insure substantially steady air flow in the tube before `the vane is left unguarded. In a copending application Serial No. 317,857 of even date herewith, I have disclosed apparatus of the. general type herein described. In the apparatus of said application the closure of the controlling valve is initiated by a timing device, but I have disclosed and claimed therein certain structural details common to the two devices and have limited the present application in general to those features which are concerned with control through variation in air velocity.

In the accompanying drawings in which I have illustrated one desirable embodiment of the invention byway ofexample Fig. l is a fragmentary elevation` illustrating part of the central station desk of a pneumatic despatch system having-my improved power control' apparatus-applied thereto;

Fig. 2 is a fragmentary vertical section, to larger scale, showing details of the power control apparatus with its parts in normal position, that is to say, with the controlling valve closed;

Fig. 3 is a view similar to Fig. 2 but showing the controlling valve-wide open and indi eating the detector device, which initiates closure of the controlling valve, in its operative or sensitively responsive position;

Fig. 4 is a view-similar to Fig.` 3 showing the controlling valve Vopen but showing the detector device in position to initiate closure of the controlling valve;

Fig. 5 is a" view similar toI F-ig. 4 but showing the'controlling valve closed and an auxiliary valve still in closed position;

Fig. 6 is a fragmentary side elevation of the controlling apparatus7 illustrating details of means for closing a pilot valve;

FiO. 7 is a fragmentary section substantially) on the line 7-7 of Fig. 3 showing details of the detector device;

Fig. 8 is a fragmentary section of a device generally similar to that shown in Fig. 4, but illustrating a modified form of deflect-or.

Referring to the drawings, the numeral 1 indicates a fragmentary section of the central station desk of a pneumatic despatch system comprising transmission tubes, such for example as the tube 2, which lead from the central station desk. Each tube 2 is furnished with a delivery terminal 3 and is provided with a continuation 4 connecting it to an individual power control device indicated generally by the numeral 5. This power control device is connected by means of a suction tube 6 to a vacuum drum or header 8 in which a low pressure is continuously maintained by means of a suitable pump, exhauster, or equivalent apparatus, not shown.

An open ended despatch terminal 9 corresponding to each tube 2 is provided at the central station, such despatch terminal forming the entrance to that run of the tube which leads to the corresponding remote sending station. A continuous air passage or conduit is thus provided extending from the terminal 9 tothe exhauster, that portion of the conduit provided by the tubes which lead to and from the remote station constituting the carrier transmission line. The above arrangement in general is old and well known and requires no further specific description, the present invention being confined to improvements in the power control apparatus per se.

Referring to Figs. 2 and 3, the power control apparatus comprises a casing 10, preferably of more or less cylindrical form, having upper and lower parts 11 and 12 adapted to receive the lower end of the tube 4 and the upper end of the tube 6 respectively. Casing 10 has a passage 13 which is aligned with the tubes 4 and 6, thus forming an intermediate portion of the air conduit.

A shaft 14 extends transversely across the passage 13, being journaled in suitable bearings in the walls of thecasing 10. This shaft carries a controlling or main valve 15, preferably of butterfly type, which in closed position is preferably inclined to the axis of the conduit as shown in Fig. 2. Preferably the upper wing of the valve is of slightly greater area than the lower wing so that the air pressure tends to hold the valve closed.

Preferably one end of the shaft 14 projects beyond the outer surface of the casing and is provided with an arm 16 adapted to engage a stop pin 17a (Fig. 6) when the valve is in its fully open position. 7h-en in the latter position the valve is preferably inclined slightly to the axis of the passage 13, as shown in Fig. 3, so that the pressure of the air against the upper surface of the valve is suflicient to hold it open.

A passage 17 formed in the substance of the casing 10 provides a by-pass around the closed valve 15 to permit a constant but slight flow of air, known in the art as the minimum How. The passage 17 may be adjusted by means of the screw 18 having a head 19 preferably engaged by a detent 2O to hold it in an adjusted position.

At one side of the casing I provide a housing consisting of the parts 21 and 22 between which the edge portion of a diaphragm 23 is clamped. This diaphragm divides the space within the housing into chambers C and C1. The chamber C communicates with the outer atmosphere through an opening P. The housing which contains the main diaphragm is provided with a bleeder passage 63 controlled by an adjustable screw 64.

The central part of the diaphragm is clamped to a sliding stem 24, movable in guide openings in the members 21 and 22, and the outer end of this stem is provided with acollar or flange 25 engaging the forked end 26 of a lever 27 fulcrumed at 28 on a bracket 29 projecting from the member 22. This lever has an angularly disposed arm 30 to which one end of a spring 31 is connected. The other end of the .spring is secured to an adjustable anchorage member 32 carried by a bracket 33 upon thepart` 22.

The stem 24 is provided with an extension 34, preferably of smaller diameter, which slides in a guide opening in the wall 0f the casing 10 and enters a chamber 35 in said wall. The extension 34 preferably terminates in a tail portion 36 of still smaller diameter.

The extension 34 passes freely through an opening 37 in the lower wing of the valve 15, and where the extension 34 joins the stem 24 a shoulder 38 (Figs. 2, 3 and 4) is formed which constitutes an actuating abutment engageable with the valve 15 for moving the latter to open position. As the valve passes the vertical position, the air current flowing through the tube swings it slightly to thel right beyond the vertical position as above described. l

The chamber C1 normally communicates by a passage P1 with the passage 13 in the casing 10, and an auxiliary valve 39 controls the passage P1. This auxiliaryvalveis mounted on a stem 40 sliding in suitable bearings carried by the casing 10, and at its opposite end enters the housing of an auxiliary pneumatic, said houisng comprising parts 41 and 42 which clamp the edges of a diaphragm 43 between them. This diaphragm divides the space between the housing into chambers 44 and 45, the latter communicating with the outer atmosphere through a port 46'. The chamber 44 is connected by means of a passage 47 with the chamber 35 above described, which in turn is connected to the passage 13, below the valve 15, by means of a passage 49. An adjusting screw 48 controls the sizeof the passage 47.

A pilot valve 50 normally seats against the casing at the outer end of the chamber 35, thus closing the latter against entry of atmospheric pressure, while a spring 51 within the chamber 35 tends to push the valve 50 away from its seat. The valve slides freely upon the tail portion 36 of the stem 24, and is normally held in closed position by engagement with a collar 52 preferably integral with a link 53 whose opposite end is pivotally secured to the lever arm 16.

The central part of the diaphragm 43 is secured to a sleeve l/V which slides freely on an extension Q of the steam 40, such extension being of smaller diameter than the main part of the stem, thus providing an abutment shoulder at 55 (Fig. 3). A nut 56, provided upon the outer end of the part Q, forms a second abutment for the sleeve 1V. A spring S within the chamber 44 tends constantly to move the diaphragm 43 to the left, as viewed in Fig. 2.

A shaft 57 is journaled in suitable bearings at one side of the casing 10 and this shaft carries a hub member 58 (Fig. 7) which sup ports an arm 59, preferably of stiff wire and of hair-pin shape, carrying at its upper end a vane 60. This arm 59 straddles the stem 40 of the valve 39, and the stem 40 carries an abutment member 61 adapted, under certain conditions, to engage the arm v59 and thus to determine the position of the vane 60. The sleeve 57 extends outwardly beyond the wall of the casing and is furnished with a spring 62 which tends to swing the arm 59 in a clockwise direction, as viewed in Fig. 2.

The operation of the apparatus is substantially as follows, it being assumed that when the transmission line is empty, that is to say, when n0 carrier is passing, the various parts of the power controlling device occupy substantially the positions indicated in Fig. 2. In this figure the main valve 15 is closed and a minimum flow of air is passing through the port 17 g the diaphragm 23 is in its righthand position; the valve 39 is open, thus providing communication between the passage 13 and the chamber C1; and the valve 50 is closed and atmospheric pressure, acting on the left-hand side of a diaphragm 43, holds the latter in the position shown in Fig. 2 against the action of spring S. At the same time the spring 62 (Fig. 7) holds the arm 59 in Contact with the limiting stop 61. The latter is now so positioned as to permit the arm 59 '1 to stand nearly upright so that the vane 60 makes such an acute angle to the axis of the passage 13 that it is not affected by air flowing at normal carrier-impelling velocity through the passage.

W'hen a carrier is introduced, either at the terminal 9 or at the outlying station, the minimum iiow in the transmission line is substantially cut off so that the pressure in the chamber C1 decreases and the diaphragm 23 moves to the left under the action of atmospheric pressure. After the diaphragm has moved a predetermined distance the 'shoulder 38 engages the valve 15, whereupon further movement ofthe diaphragm swings the valve to and slightly beyond the vertical position, as viewed in Fig. 3. As the valve passes the vertical position it is caught by the air curn rent which tends to swing it further in a clockwise direction, its movement being limited by engagement of the arm 16 with the stop 17.

As the valve 15 approaches its open position, the abutment shoulder 54 engages the valve 5() and moves the latter from its seat, whereupon the spring 51 continues the out ward movement of the valve until it is stopped by engagement with the member 52. As soon as the valve 50 is unseated, air enters the chamber 44 through the passage 47 `at a predetermined slow rate in accordance with the setting of the screw 48. The spring S is thus ultimately able to move the diaphragm 43 to the left, and when the sleeve WV strikes the abutment 56 the stem 4() is moved to the left, closing the valve 39. At the same time the stop 61 moves to the left, swinging the vane 6() to the position shown in Fig. 3. Since this movement of -the vane does not take place immediately upon opening of the valve 15 but only at the end of a predetermined in terval of time thereafter, the air current in the passage 13 has time to become steady and of substantially uniform velocity before the vane is moved over to its sensitive or operative position, as illustrated in Fig. 3.

During the flight of the carrier through the tube, air gradually leaks into the chamber C1 through the opening 63, building up pressure therein until'eventually the'spring '31 is able to move the stem 24 andthe diaphragm 23 to the right, as shown in Fig. 4. Since the stem 24 of the diaphragm is not 'connected to the valves 15 and 50 'in such a way asr to move them with it to the right, these valves are left standing in open position and the valve 39 remains closed.

When the lcarrier emerges from the line, the sudden resulting rush of air or increase in air velocity in the tube causes the vane or deflector 60 to swing downwardly, as shown in Fig. 4, until itvengages the opposite wall of the passage. Vvlhen in' this position the vane 60 acts as a deflector, diverting the air current toward the right-hand side of the casing, as shown by the arrows in Fig. 4, and the current of air which 'encounters the righthand face of the valve 15 exerts sufficient pressure thereon to swing the valve to the closed position shown in Fig. 5. As the valve 15 closes, the lever arm 16 pulls on the link 53 and closes the valve 50. Theair is now slowly sucked out of the chamber 44, whereupon air pressure on theleft-hand side of diaphragm 43 movesthe latter to the right until after 'an' interval it engages the shoulder 55 and moves the stein 40 to the right, opening the valve 39 and permitting the vane 6() to resume its inoperative or non-sensitive position. The partsare thus restored to their original position ready for a repetition of the operation.

In F ig. 8 I have illustrated a slight modification wherein, in place ot the movable vane 60, I have provided a fixed deflector 65. By proper adjustment and proportioning of the parts, it is possible so to arrange a fixed detleotor of this type that when the air current is flowing at carrier impelling velo-city through the tube, the main valve being open, the current will not be diverted to a suiicient extent to close the main Valve, but when the velocity ot the current increases beyond the normal amount (at the delivery of the carrier from the tube) the increased velocity results in increased or sharper deviation of the air Icurrent from the deilector 65, suilicient to cause the air to bear against the right-hand side of the valve and thereby to close the latter. VJhile this iXed type of deflector may be useful under some circumstances, it must necessarily be arranged with great accuracy,

and I prefer the movable deiiector or vane disclosed in the preceding views.

Although I have heroin disclosed certain desirable embodiments of the invention, I wish it to be understood that various changes in detail, for example in the size, shape or relative arrangement ot parts or the substitution of equivalents, may be made Without departing from the invention.

I claim:

l. Power controlled apparatus for use in a pneumatic despatch system having a transmission tube, said apparatus comprising a controlling` valve which, when open, is held motionless by the pressure of the air against one side of it, andmeans responsive to delivery of a carrier from the transmission tube to cause the air pressure to shift to the other side of the valve and thereby close it. Y

2. kPower control apparatus ot the class described comprising a controlling valve, motor means for moving it to open position, and means operative upon delivery of a carrier, to direct a current ot' air against the valve in such a direction as to close it.

3. Power control apparatus of the class described comprising a controlling valve of but tertly type which, when open, is slightly inclined to the air current and is held in open position by the pressure ot the current against one side of it, and deliector means responsiveV toabnormal velocity of air flow to divert the air current against the other side of the valve to close the latter.

4. Power control apparatus comprising` a controlling valve, a pneumatic, and means actuated thereby to open the valve as the pneumatic moves in one direction, said means being inefective to actuate vthe valve as the pneumatic moves in the opposite direction,

and means actuable upon delivery of a carrier to direct a current of air against the valve to close it.

5. Power control apparatus of the class described comprising a controlling valve which, when open, is held in position by the pressure of the air current against one side of it, and a detlector which is inoperative when fexposed to normal air flow but which moves in response to abnormal air velocity and after so moving deliects the air current against the opposite side of the valve, therebyA closing the latter.

6. Power control apparatus of the class described comprising a controlling valve which, when open, is held in position by the pressure of the air current against one side of it, and a swinging detlector vane normally disposed in inoperative position, said vane swinging in response to abnormal velocity of air flow and after so swinging acting to deflect the air current against the opposite side of the valve to close the latter.

7. Power control apparatus of the class describen comprising a controlling valve which, when open, is held in position by the pressure ot the air current against one side ot it, a swinging deiector vane, a spring tending to move the vane to an inoperative position, and a stop for limiting such movement, the vane remaining substantially stationary during normal'tlow of the air current but swinging awayfrom the stop in response to abnormal air velocity and after so moving acting' to de- Heet the air current against the opposite side of the valve to close the latter'.

8. Power control apparatus for pneumatic despatch system of the vacuum minimum How type having a transmission tube and an exhauster, said apparatus comprising a valve i'or controlling carrier impelling air flow in the transmission tube, a minimum flow of air through the transmission tube being at all imes permitted, means 'for opening the valve,

detector means for initiating closure of the valve, said detector means being substantially unresponsive to conditions in the tube resulting from opening the valve but becoming suiiiciently sensitive, a predetermined time after opening oi' the valve, to respond to conditions resulting from delivery oitl a carrier from the tube.

9. Power control apparatus for a 'pneumatic des'atch system of the vacuum minimum How type having a transmission tube and an exhauster, said apparatus comprising a valve for controlling carrier impelling air iiow in the transmission tube, a minimum flow of airf through the transmission tube being at all times permitted, means oropening the valve, detector means for initiating closure of the valve, and means substantially preventing response of said detector to changing conditions inthe tube until after the valve has been open for a predetermined time.

llO

10. Power control apparatus for a pneumatic despatch system ot the vacuum minimum flow type having a transmission tube and,an ezrhauster, said apparatus comprising a valve for controlling carrier impelling air ilow in the transmission tube, a minimum flow ot air through the transmission tube being at all times permitted, means for opening the valve, and detector means for initiating closure of the valve, said detector means being less sensitively responsive to fluctuating conditions in the transmission tube betore the opening oiA the valve than after the establishment of steady carrier impelling air flow in the tube.

ll. Power control apparatus for a pneumatic despatch system of the vacuum minimum iow type having a transmission tube and an exhauster, said apparatus comprising a valve for controlling carrier impelling air flow in the transmission tube, a minimum flow of air through the transmission tube being at all times permitted, means for opening the valve, detector means for initiating closure oit the valve, said detector means being substantially unresponsive to fluctuating conditions in the tube resulting from opening of the valve, and means for making the detector more sensitive after the valve has been open for a predetermined time.

12. Power control apparatus for a pneumatic despatch system of the vacuum mini-,

mum flow type having a transmission tube and an exhauster, said apparatus comprising ay valve for controlling carrier impelling air flow in the transmission tube, a minimum flow of air through the transmission tube being at all times permitted, means for opening the valve, detector means for initiating closure of the valve, said detector tending to respond to fluctuations in air velocity in the tube, and means substantially preventing such response until a predetermined time after the valve has opened.

13. Power control apparatus Jfor a pneumatic despatch system of the vacuum minimum flow type having a transmission tube and an exhauster, said apparatus comprising a valve for controlling carrier impelling air liow in the transmission tube, a minimum low ot air through the transmission tube being at all times permitted, means for opening the valve, detector means for initiating closure of the valve, said detector comprising a vane exposed to the air flowing in the tube, and means substantially preventing eective action of the air current upon the vane during and for a predetermined period after opening of the valve.

14. Power control apparatus for a pneumatic despatch syst-em of the vacuum minimum How type having a transmission tube and an exhauster, said apparatus comprisingl a valve for controlling carrier impelling air low inthe transmission tube, a minimum,v

flow of air through the transmission tube being at all times permitted, means for opening the valve, detector means for initiating closure of the valve, said detector means comprising an element exposed to the airin the tube, and means for holding said element in such a` position, during and for a predetermined period a'fter opening of the valve, as to prevent effective action ot' the air thereon.

15. Power control apparatus for a pneumatic despatch system ot the vacuum minimum flow type having a transmission tube and an exhauster, said apparatus comprising a valve for controlling carrier impelling air flow in the transmission tube, a minimum flow of air through the transmission tube being at all times permitted, means for opening the valve, detector means for initiating closure of the valve, said detector comprising a vane exposed to the air flowing in the tube, and means tending to hold the vane at such an angle to the air current, during and for a predetermined period after opening of the valve, that fluctuations in velocity of air current due to opening oi' the valve do not actuate the vane.

16. Power control apparatus for a pneumatic despatch system of the vacuum minimum flow type having a transmission tube and anexhauster, said apparatus comprising a valve 'for controlling carrier impelling air flow in the transmission tube, a minimum iiow of air through the transmission tube being at all times permitted, means for opening the valve, detector means for initiating closure ot the valve, said detector comprising a vane exposed to the air flowing in the tube, means tending normally to hold the vane at such an angle to the air current that it is not operatively affected by fluctuations in the current, and means acting a predetermined time after opening of the valve, for swinging said vane to a position more nearly at right angles to the current.

17. Power control apparatus for a pneumatic despatch system ot the vacuum minimum flow type having a transmission tube and an exhauster, said apparatus comprising a valve for controlling carrier impelling air liow in the transmission tube, a minimum iiow of air through the transmission tube being at all times permitted, means for opening the valve, detector means for initiating closure ot the valve, said detector comprising a swinging vane, a spring tending to swing said vane toward a position in which it is parallel to the air iiow, and means movable a predetermined time after the opening of the valve for swinging the vane to a position such that it becomes sensitively responsive to fluctuations in air velocity in the tube.

18. Power control apparatus for a pneumatic despatch system of the vacuum minimum flow type having a transmission tube and an exhauster, said apparatus compris- Cir ing a valve for controlling carrier impelling air flow in the transmission tube, a minimum iiow of air through the transmission tube being at all times permitted, means for opening the valve, the valve being retained 1n open position by the pressure of the normally flowing air current, and means to deflect air flowing at abnormal velocity through the tube into contact with the open valve so as to close the latter.

19. Power control apparatus for a pneumatic -despatch system of the vacuum minimum flow type having a transmission tube and an exhauster, said apparatus comprising a valve for controlling carrier impelling air flow in the transmission tube, a minimum flow of air through the transmission tube being at all times permitted, means for opening the valve, the valve being retained in open position by the pressure of the normally flowing air current, and means responsive to the delivery of a carrier from the tube for diverting lthe flowing air current into a path such that it closes the valve.

20. Power control apparatus for a pneumatic despatch system of the vacuum minimum flow type having a transmissiontube and an eXhauster, said apparatus comprising a valve for controlling carrier impelling air flow in the transmission tube, a minimum flow of air through the transmission tube being at all times permitted, means for opening the valve, the valve when open being held in such position by the pressure of the current thereagainst, and normally inoperative deflector means including a vane eX- posed to the air current in the tube, said deilector responding to abnormal air velocity in the tube and moving to a position such as to deflect the air current against the side of the valve thereby closing the latter.

21. Power control apparatus for a pneumatic despatch system of the vacuum minimum flow type having a transmission tube and an exhauster, said apparatus comprising a valve for controlling carrier impelling air flow in the transmission tube, a minimum flow of air through the transmission tube being at all times permitted, means for opening the valve to a position such that the pressure of the air current thereagainst tends to hold it open, and a movable deflector normally disposed in inoperative position adjacent to one side of the tube, said deflector moving to a position adjacent to the lopposite side of the tube in response to abnormal air velocity in the tube, and when in the latter position so diverting the air current as to cause it to close the valve.

22. Power control apparatus for a pneumatic despatch system of the vacuum minimum flow type having a transmission tube and an exhauster, said apparatus comprising a valve for controlling carrier impelling air flow in the transmission tube, a minimum flow of air through the transmission tube being at all times permitted, means for opening the valve, a motor means responsive to introduction of a carrier into the tube to move the valve to open position, detector means responsive to discharge of a carrier from the tube to initiate closure of the valve, and means for guarding said detector means from the effects of opening the valve and for guarding the motor means from the effects of closing the valve.

23. Power control apparatus for a pneumatic despatchsystem of the vacuum minimum flow type having a transmission tube and an eXhauster, said apparatus comprising a valve for controlling carrier impelling air flow in the transmission tube, a minimum flow of air through the transmission tube being at all times permitted, means for opening the valve, a pneumatic responsive to introduction of a carrier into the tube to move the valve to open position, detector means responsive to discharge of a carrier from the tube to initiate closure of the valve, and means for guarding said detector means from the effects of opening the valve and for guarding the pneumatic from the effects of closing the valve, said guard means comprising an auxiliary pneumatic, and means for timing its operation relatively to that of the controlling valve.

2li. Power control apparatus for a pneumatic despatch system of the vacuum minimum flow type having a transmission tube and an exhauster, said apparatus comprising a valve for controlling carrier impelling air low in the transmission tube, a minimum flow of air through the transmission tube being at all times permitted, means for opening the valve, a pneumatic responsive t-o introduction of a carrier into the tube to move the valve to open position, detector means responsive to discharge of a carrier from the tube to initiate closure of the valve, and means for guarding said detector means from the effects of opening the valve and for guarding the pneumatic from the effects of closing the valve, said guard means comprising a normally open auxiliary valve for shutting off the pneumatic from the tube after the f controllingvalve opens and an element for holding the detector means inoperative until after the controlling valve opens.

25. Power control apparatus for a pneumatic'despatch system of the vacuum minimum flow type having a transmission tube and an eXhauster, said apparatus comprising a valve for controlling carrier impelling air flow in the transmission tube, a minimum flow of air through the transmission tube being at all times permitted, means for opening the valve, a pneumatic responsive to introduction of a carrier into the tube to move the valve to open position, detector 'means responsive to discharge of a carrier from the tube to initiate closure of the valve, andmeans for guarding said detector means from the effects of opening the valve and for guarding the pneumatic from the effects of closing the valve, said guard means comprising a normally open auxiliary valve for shutting ot the pneumatic from the tube, an auxiliary pneumatic which acts a predetermined time after the controlling valve opens to close the auxiliary valve, and means controlled by said auxiliary pneumatic to render the detector operative as the auxiliary valve closes.

26. Power control apparatus for a pneumatic despatch system of the vacuum minimum flow type having a transmission tube and an exhauster, said apparatus comprising a valve for controlling carrier impelling air flow in the transmission tube, a minimum iiowA of air through the transmission tube being at all times permitted, means for opening the valve comprising a main pneumatic, a normally open auxiliary valve for cutting oil the pneumatic from the tube, an auxiliary pneumatic for determining the closure of the auxiliary valve, a pilot valve for initiating movement of the auxiliary pneumatic, a member connected to the main pneumatic and operable as the latter moves in one direction to open the controlling valve and the pilot valve, said valves remaining open as the pneumatic returns toward normal position, the controlling valve closing in response to delivery of a carrier from the tube, and means actuated by the controlling valve for closing the pilot valve.

27. Power control apparatus for a pneumatic despatch system of the vacuum minimum loW type having a transmission tube and an exhauster, said apparatus comprising a valve for controlling carrier impelling air flow in the transmission tube, a minimum How of air through the transmission tube being at all times permitted, means for opening the valve comprising a main pneumatic, a normally open auxiliary valve for cutting off the pneumatic from the tube, an auxiliary pneumatic for determining the closure of the auX- iliary valve, a pilot valve for initiating movement of the auxiliary pneumatic, a member connected to the main pneumatic and operable as the latter moves in one direction t0 open the controlling valve and the pilot valve, said valves remaining open as the pneumatic returns toward normal position, means vfor directing a blast of air against the controlling valve to close the latter, and connections between the controlling valve and pilot valve for closing the latter as the controlling valve closes.

Signed by me at Syracuse, New York, this Q-lth day of Cctober, 1928.

JAMES T. GOWLEY, 

